Identification of rubella virus T-cell epitopes recognized in anamnestic response to RA27/3 vaccine: associations with boost in neutralizing antibody titer

How to determine protective immunity in the post-vaccine era

The ability to determine an individual's susceptibility to infection relies heavily on the assay used, and the ability to correlate results of the assay to a clinical interpretation. Current rubella immunity screening methods identify total rubella IgG antibodies circulating in the serum, however both humoral and cell mediated immune responses have been shown to contribute to protection from infection. Therefore, antibody screening assays may under-estimate immunity in some populations. In fact, waning antibody titers over time in a large prenatal population were recently documented in North America, and the trend has been echoed in other countries that have achieved elimination through universal rubella vaccination. Despite decreasing antibody titers, the number of acute rubella cases has not increased in these populations, suggesting that the lower antibody levels may still be protective. Based on the changing epidemiology in universally vaccinated populations, it may be time to reassess the level of antibody that indicates immunity to rubella infection.

Rubella specific cell-mediated and humoral immunity following vaccination in college students with low antibody titers

OBJECTIVE

This study measured cell-mediated immunity (CMI) and antibodies to clarify the basis of rubella reinfection after vaccination.

METHODS

In a pool of 65 college students, 39 who exhibited hemagglutination-inhibition (HI) antibody titers against rubella of ≤ 1:16 were vaccinated with a rubella vaccine. The CMI was assessed with interferon-gamma release assay.

RESULTS

There was low correlation (r = 0.24) between the antibody titers and interferon-gamma levels at pre-vaccination status. Preexisting interferon-gamma levels were low in some subjects with low HI antibody titers of 1:8 and 1:16. Fifty-seven percent (4/7) of the subjects who were antibody-negative with past history of rubella vaccination at entry onto the study exhibited CMI. And 57% (4/7) of the subjects remained antibody-negative following a second vaccination, despite exhibiting CMI. HI antibody titers increased significantly after vaccination, whereas post-vaccination interferon-gamma levels did not exhibit significant increases. When subjects were divided (based on their past history of vaccination and antibody values) into natural infection and vaccination groups, HI antibody titers (mean ± SD) increased to 1:2(4.4 ± 1.4) from 1: 2(3.2 ± 0.4) (p = 0.065) in the natural infection group and to 1:2(4.4 ± 1.0) from 1:2(3.0 ± 0.8) (p < 0.00001) in the vaccination group following vaccination. The same classification revealed that interferon-gamma values did not increase significantly in either group following vaccination, but the interferon-gamma values at pre- and post-vaccination in the natural infection group were significantly higher than those at pre- and post-vaccination in the vaccination group (p < 0.05 and p < 0.05, respectively).

CONCLUSION

Pre-vaccination interferon-gamma levels in each HI antibody titer group were similar. And there were some subjects with antibody-positive exhibited CMI-negative. These data may explain why rubella reinfection can occur in vaccinated seropositive individuals.

Genetic polymorphisms associated with rubella virus-specific cellular immunity following MMR vaccination

Rubella virus causes a relatively benign disease in most cases, although infection during pregnancy can result in serious birth defects. An effective vaccine has been available since the early 1970s and outbreaks typically do not occur among highly vaccinated (≥2 doses) populations. Nevertheless, considerable inter-individual variation in immune response to rubella immunization does exist, with single-dose seroconversion rates ~95 %. Understanding the mechanisms behind this variability may provide important insights into rubella immunity. In the current study, we examined associations between single nucleotide polymorphisms (SNPs) in selected cytokine, cytokine receptor, and innate/antiviral genes and immune responses following rubella vaccination in order to understand genetic influences on vaccine response. Our approach consisted of a discovery cohort of 887 subjects aged 11-22 at the time of enrollment and a replication cohort of 542 older adolescents and young adults (age 18-40). Our data indicate that SNPs near the butyrophilin genes (BTN3A3/BTN2A1) and cytokine receptors (IL10RB/IFNAR1) are associated with variations in IFNγ secretion and that multiple SNPs in the PVR gene, as well as SNPs located in the ADAR gene, exhibit significant associations with rubella virus-specific IL-6 secretion. This information may be useful, not only in furthering our understanding immune responses to rubella vaccine, but also in identifying key pathways for targeted adjuvant use to boost immunity in those with weak or absent immunity following vaccination.

SNP/haplotype associations in cytokine and cytokine receptor genes and immunity to rubella vaccine

An effective immune response to vaccination is, in part, a complex interaction of alleles of multiple genes regulating cytokine networks. We conducted a genotyping study of Th1/Th2/inflammatory cytokines/cytokine receptors in healthy children (n = 738, 11-19 years) to determine associations between individual single-nucleotide polymorphisms (SNPs)/haplotypes and immune outcomes after two doses of rubella vaccine. SNPs (n = 501) were selected using the ldSelect-approach and genotyped using Illumina GoldenGate and TaqMan assays. Rubella-IgG levels were measured by immunoassay and secreted cytokines by ELISA. Linear regression and post hoc haplotype analyses were used to determine associations between single SNPs/haplotypes and immune outcomes. Increased carriage of minor alleles for the promoter SNPs (rs2844482 and rs2857708) of the TNFA gene were associated with dose-related increases in rubella antibodies. IL-6 secretion was co-directionally associated (p < or = 0.01) with five intronic SNPs in the TNFRSF1B gene in an allele dose-related manner, while five promoter/intronic SNPs in the IL12B gene were associated with variations in IL-6 secretion. TNFA haplotype AAACGGGGC (t-statistic = 3.32) and IL12B promoter haplotype TAG (t-statistic = 2.66) were associated with higher levels of (p < or = 0.01) rubella-IgG and IL-6 secretion, respectively. We identified individual SNPs/haplotypes in TNFA/TNFRSF1B and IL12B genes that appear to modulate immunity to rubella vaccination. Identification of such "genetic fingerprints" may predict the outcome of vaccine response and inform new vaccine strategies.

Correlation between rubella antibody levels and cytokine measures of cell-mediated immunity

Despite a safe and effective vaccine, endemic rubella remains a problem in developing countries. Isolated cases and outbreaks can occur in areas with high vaccine coverage. Individuals, especially pregnant women who remain unimmunized or do not seroconvert, are susceptible to infection and their infants are at risk for congenital rubella syndrome (CRS). Both humoral and cellular immune responses contribute to immune protection. Classically, immunity to rubella has been assessed through the detection of rubella-specific antibody titers. In this study we examined correlates of both humoral and cellular immunity in a large population of immunized young adults in Olmsted County, MN. We were unable to find any significant correlation between cytokine production after in-vitro rubella stimulation and serum antibody titers.

Predominant inflammatory cytokine secretion pattern in response to two doses of live rubella vaccine in healthy vaccinees

We conducted a population-based study on 738 schoolchildren who received two doses of rubella vaccine in order to determine cytokine secretion patterns and their associations with demographic and clinical variables. The results showed a robust rubella-specific inflammatory cytokine response characterized by high median [inter-quartile range (IQR)] secretion levels (in pg/mL) of IL-6 [3681.0 (3160.0, 4052.0)], GM-CSF [28.0 (23.6, 32.6)], and TNF-alpha [29.7 (-7.0, 89.2)]. We also detected modest levels of rubella-specific secretion of Th1 cytokines IL-2 and IFN-gamma, while IL-12p40 was undetectable. In contrast, rubella-specific Th2 responses were hardly detectable. Age at vaccination, enrollment, and time elapsed between last vaccination and enrollment was significantly associated with the outcome of IL-2, IL-6, and IFN-gamma secretion. These results suggest an immune-deviation or "skewing" from Th1/Th2 cytokine patterns towards a predominant inflammatory response upon in vitro rubella virus stimulation.

Effect of human leukocyte antigen homozygosity on rubella vaccine-induced humoral and cell-mediated immune responses

Human leukocyte antigen (HLA) genes play a critical role in host immunity, including vaccine responses. HLA molecules present antigenic peptides to T cells and provide inhibitory signals to NK cells, and polymorphisms within HLA genes allow binding and presentation of a diverse array of self and foreign peptides. Heterozygosity across HLA alleles has been found to play a positive role in host defense for a variety of infections. Homozygosity within one or more HLA loci may restrict this epitope repertoire and limit T-cell responses to infection or vaccination. Here we report that homozygosity within the HLA DPB1 locus is associated with increased levels of rubella-specific IgG, an effect driven by a common allele DPB1*0401. We also show that homozygosity within different HLA class I and class II loci is correlated with variations (but not necessarily decreases) in interleukin (IL)-2, IL-5, and IL-10 secretion after rubella virus stimulation.

Phylogenetic analysis of rubella virus strains from an outbreak in Madrid, Spain, from 2004 to 2005

An outbreak of rubella affected 460 individuals in 2004 and 2005 in the community of Madrid, Spain. Most of the patients were nonvaccinated Latin American immigrants or Spanish males. This study presents the first data on rubella virus genotypes in Spain. Forty selected clinical samples (2 urine, 5 serum, 3 blood, 2 saliva, and 28 pharyngeal exudate samples) from 40 cases were collected. The 739-nucleotide sequence recommended by the World Health Organization obtained from viral RNA in these samples was analyzed by using the MEGA v4.0 software. Seventeen isolates were obtained from 40 clinical samples from the outbreak, including two isolated from congenital rubella syndrome cases. Only viral RNA of genotype 1j was detected in both isolates and clinical specimens. Two variations in amino acids, G253C and T394S, which are involved in neutralization epitopes arose during the outbreak, but apparently there was no positive selection of either of them. The origin of the outbreak remains unknown because of poor virologic surveillance in Latin America and the African countries neighboring Spain. On the other hand, this is the first report of this genotype in Europe. The few published sequences of genotype 1j indicate that it comes from Japan and the Philippines, but there are no epidemiological data supporting this as the origin of the Madrid outbreak.

Relationship between HLA polymorphisms and gamma interferon and interleukin-10 cytokine production in healthy individuals after rubella vaccination

We studied the association between HLA alleles and rubella-specific gamma interferon (IFN-gamma) (Th1) and interleukin-10 (IL-10) (Th2) cytokine responses among 106 healthy children (ages, 14 to 17 years) previously immunized with two doses of rubella vaccine. Antibody titers and cytokine responses to rubella vaccination were not sex or age dependent. Several class I HLA-A (*0201, *2402, *6801) alleles were significantly associated with rubella vaccine-induced IFN-gamma secretion. Several class II HLA-DRB1 (*0101) and HLA-DQB1 (*0501) alleles were also suggestive of an association with IFN-gamma secretion. Alleles with potential associations with rubella-specific IL-10 production included HLA-A (*0201, *6801), HLA-B (*4901), and HLA-DRB1 (*1302). The class I A*0201 and A*6801 alleles were associated with both IFN-gamma and IL-10 secretion. These tentative associations need to be validated in larger studies with subjects of differing ethnicities. These results provide additional evidence that HLA genes may influence Th1- and Th2-specific cytokine response(s) following rubella immunization, which in turn can influence both cellular and humoral immune responses to rubella vaccination.

Significance of avidity and immunoblot analysis for rubella IgM-positive serum samples in pregnant women

A total of 512 IgM-positive serum samples from 449 pregnant women referred by microbiologists and medical laboratories for additional testing and final interpretation were collected over a 3-year period. Employment of an IgM capture enzyme immunoassay (EIA) confirmed only 31% of the initial EIA-IgM-positive samples. In order to discriminate acute rubella virus infections, which are associated with increased risk of fetal infection and embryopathy, from persistent or non-specific IgM, IgG avidity index and the presence of IgG with specificity to rubella virus E2 glycoprotein was determined by Western immunoblot. In only six patients (1.3%), a primary infection with rubella virus was diagnosed on the basis of IgM positivity, low avidity IgG, absence of E2-specific IgG in immunoblot concordant with clinical findings as well as consistent changes in follow-up samples. The serological results were not compatible with rubella re-infection. The infection status in 14 patients (3.1%) remained inconclusive even when both avidity assay and immunoblot were used, while restriction to either test did not allow a conclusive interpretation in 11.6% of patients. The use of both assays is clearly better, and therefore, recommended in IgM-positive samples.

Correlates of lymphoproliferative responses to measles, mumps, and rubella (MMR) virus vaccines following MMR-II vaccination in healthy children

Cell-mediated immunity (CMI) to measles, mumps, and rubella viral antigens plays a critical role in providing long-term protection against these infectious diseases. We examined CMI by measuring lymphoproliferative response induced in response to stimulation with the above three antigens following two doses of measles, mumps, and rubella-II (MMR-II) vaccine in a randomly selected, population-based cohort of healthy children. We determined if a correlative and predictive intraclass relationship exists between CMI to the three components of MMR-II. We detected positive lymphoproliferative responses to measles, mumps, and rubella vaccines. Mumps vaccine used as an antigen had the highest median stimulation index followed by measles and rubella vaccines. The overall intraclass correlation value for lymphoproliferative response to measles, mumps, and rubella using Pearson's correlation was 0.61 (95% confidence interval = 0.56, 0.66). We observed a significant pairwise association to individual vaccine components between subjects in the upper and lower 10th percentile of immune response. This study demonstrates recall CMI post-MMR-II vaccination with significant intraclass correlation among the CMI responses to the three vaccine components.

The contribution of HLA class I antigens in immune status following two doses of rubella vaccination

The variability of humoral and cellular immune responses modulated by human leukocyte antigen (HLA) genes is a significant factor in the protective effect of rubella vaccines. We performed HLA class I typing in a group of 346 healthy schoolchildren and young adults who previously received two doses of measles-mumps-rubella-II vaccine. Rubella virus-specific humoral (serum antibody) immunity and cell-mediated immunity (lymphocyte proliferation) were assessed. Median values for antibody levels and stimulation indices (SI) were 38.63 IU/ml and 2.29 IU/ml, respectively. The alleles that provided suggestive, but not conclusive, evidence of HLA association with rubella seropositivity were HLA-B*2705 (median, 24.68 IU/ml; p = 0.160), B*4501 (median, 61.22 IU/ml; p = 0.098), Cw*0303 (median, 30.34 IU/ml; p = 0.102) and Cw*0704 (median, 26.58 IU/ml; p = 0.144). These alleles approach, but do not achieve, statistical significance. Of all the alleles analyzed, HLA-B*3503 (median SI, 3.00; p = 0.031) and HLA-Cw*1502 (median SI, 3.19; p = 0.035) were positively associated with lymphoproliferative responses to rubella virus antigens, whereas the HLA-B*3901 (SI, 1.34; p = 0.066) allele was negatively associated. This suggests that class I HLA alleles may have limited associations with humoral and cellular immune responses to rubella vaccine. These data may facilitate our understanding of immune response variation in a genetically outbred heterogeneous population.